1. Technical Field
The field of application of this invention mainly concerns the metrological verification and the calibration of multi-dimensional measuring instruments such as three-dimensional measuring machines, without or without contact, machines with a rotary table, poly-articulated arms, and such as laser tracker type apparatuses and theodolites. The invention concerns a two-dimensional metrology standard, that is to say a calibration standard capable of serving as a metrological reference for coplanar lengths (non-parallel) and/or angles (non-zero).
2. Description of the Related Art
The geometry of a multi-dimensional measuring machine is generally verified on the basis of one-dimensional calibration standards of calibration gauge block or stepped block type, placed in different positions in the measuring space. The ISO-10360 series of standards sets a certain number of distance measurements (referred to as sizes) in different positions to verify that the maximum measurement discrepancy is less than a manufacturer's specification. This procedure is very costly in time and in number of calibration standards, and above all only enables partial verification of geometry. If it is desired to measure geometry more fully, it is necessary to provide a multiplicity of positions for the blocks, or employ an interferometer and electronic levels.
In order to simplify the process of verifying a multi-dimensional measuring machine, certain assemblies of one-dimensional calibration standards have been produced. They thus enable the geometry of the machine to be tracked by monitoring the drifts relative to an initial measurement, but these assemblies do not associate the dimensions together in the metrological sense (see the document JP-3427376 or the document US-2009/0082986, or the device called “KOBA-check sphere plate” of Kolb & Baumann GmbH & Co KG or that called “CMM Check” by Carl Zeiss Messtechnik GmbH). In fact, these assemblies only have the advantage of avoiding the operator having to dispose the various one-dimensional calibration standards in the measuring space himself. Yet the relative dimensions between the individual one-dimensional calibration standards do not enable lengths and angles to be linked in the metrological sense. At best, such assemblies are characterized on measuring machines considered to be more precise than those on which they will be used. These items of equipment enable tracking of the change in the machine over time, using control charts, for example, but do not enable the parameter of the geometry that has fluctuated to be defined, in case of drift.